linux-kernel - [PATCH V3 04/11] um: Improve panic notifiers consistency and ordering

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Date:   Fri, 19 Aug 2022 19:17:24 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, x86@...nel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, xuqiang36@...wei.com,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        linux-um@...ts.infradead.org,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Richard Weinberger <richard@....at>
Subject: [PATCH V3 04/11] um: Improve panic notifiers consistency and ordering

Currently the panic notifiers from user mode linux don't follow
the convention for most of the other notifiers present in the
kernel (indentation, priority setting, numeric return).
More important, the priorities could be improved, since it's a
special case (userspace), hence we could run the notifiers earlier;
user mode linux shouldn't care much with other panic notifiers but
the ordering among the mconsole and arch notifier is important,
given that the arch one effectively triggers a core dump.

Fix that by running the mconsole notifier as the first panic
notifier, followed by the architecture one (that coredumps).

Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
Cc: Johannes Berg <johannes@...solutions.net>
Cc: Richard Weinberger <richard@....at>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>

V3:
- No changes.

V2:
- Kept the notifier header to avoid implicit usage - thanks
Johannes for the suggestion!
---
 arch/um/drivers/mconsole_kern.c | 7 +++----
 arch/um/kernel/um_arch.c        | 8 ++++----
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 8ca67a692683..69af3ce8407a 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -846,13 +846,12 @@ static int notify_panic(struct notifier_block *self, unsigned long unused1,
 
 	mconsole_notify(notify_socket, MCONSOLE_PANIC, message,
 			strlen(message) + 1);
-	return 0;
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block panic_exit_notifier = {
-	.notifier_call 		= notify_panic,
-	.next 			= NULL,
-	.priority 		= 1
+	.notifier_call	= notify_panic,
+	.priority	= INT_MAX, /* run as soon as possible */
 };
 
 static int add_notifier(void)
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index e0de60e503b9..ae272878f692 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -247,13 +247,13 @@ static int panic_exit(struct notifier_block *self, unsigned long unused1,
 	bust_spinlocks(0);
 	uml_exitcode = 1;
 	os_dump_core();
-	return 0;
+
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block panic_exit_notifier = {
-	.notifier_call 		= panic_exit,
-	.next 			= NULL,
-	.priority 		= 0
+	.notifier_call	= panic_exit,
+	.priority	= INT_MAX - 1, /* run as 2nd notifier, won't return */
 };
 
 void uml_finishsetup(void)
-- 
2.37.2